Acoustic shielding benefits for jet noise of engineover-the-wing for conventional aircraft (CTOL) application were studied with and without forward velocity for various small-scale nozzles. These latter included convergent, bypass and mixer, with and without forward ejector, nozzles. A 13-inch free jet was used to provide forward velocity. Farfield noise data were obtained for subsonic jet velocities from 650 to 980 ft/sec and forward velocities from zero to 260 ft/sec. The studies showed that although shielding benefits were obtained with all nozzles, the greatest benefits were obtained with mixer nozzles. The absolute magnitude of the jet noise shielding benefits with forward velocity was similar to the variation in nozzle-only noise with forward velocity.
Noise tests were conducted on a large-scale cold-flow model of an engine-under-the-wing externally blown flap lift augmentation system employing a mixer nozzle. The mixer nozzle was used to reduce the flap impingement velocity and, consequently, try to attenuate the additional noise caused by the interaction between the jet exhaust and the wing flap.Results from the mixer nozzle tests are summarized and compared with the results for a conical nozzle. The comparison showed that with the mixer nozzle, less noise was generated when the trailing flap was in a typical landing setting (e.g., 600).However, for a takeoff flap setting (200), there was little or no difference in the acoustic characteristics when either the mixer or conical nozzle was used.Comparisons are also made between the flap noise results from the cold-flow facility and full-scale mixer-nozzle engine tests. A simplified method of scaling based on the flow capture area at the flap impingement point is used to scale the sound pressure level data from the two separate tests to compensate for the difference in physical size of the models.Frequency shift was accounted for by the ratio of the total equivalent diameters of the two nozzles.The results show good agreement between the spectra for the cold-flow, large-scale model and the engine tests. Overall sound pressure levels below the wing were proportional to the sixth power of the peak flap impingement velocity.
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